Systems and methods for mobile node handoff

ABSTRACT

Systems and methods for handoff of a mobile node between first and second points of attachment are provided. A communication between a first and second mobile node is optimized and conducted independent of a home agent. During the handoff process the communications directed to the mobile node performing the handoff are routed to the mobile node&#39;s home agent. Once the handoff process is complete the communication is again optimized and conducted independent of home agents.

This is a continuation of application Ser. No. 11/516,761, filed Sep. 7,2006, which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

Internet Protocol (IP) networks were originally designed to communicatepackets between a host and a corresponding node (CN). A correspondingnode can send data packets to the IP host by setting the destination ofthese packets to that of the IP host. The IP network discovers theconnectivity of the network nodes and routes the data packet usingstandard topology discovery and IP protocols such as Open Shortest PathFirst (OSPF) and Border Gateway Protocol (BGP). With the knowledge ofthe network and the IP forwarding mechanisms, data packets flow from thecorresponding node to the IP host typically along the shortest route inthe network. Current IP networks predominantly use a specific IPaddressing scheme and routing protocols known as IP version 4 (IPv4).

With the development of data applications such as Voice over IP (VoIP),Short Message Service (SMS), Multi-Media Messaging Service (MMS) inmobile networks it became necessary to extend signaling and routingprotocols to enable communication with mobile devices that can attach tothe network from anywhere via a local access point. With that objectivein mind Mobile IPv4 (MIPv4) was developed. FIG. 1 illustrates aconventional network implementing MIPv4. As illustrated in FIG. 1, amobile device 102 (hereafter called Mobile Node (MN)) is registered witha router 104 (hereafter called Home Agent (HA)). Home agent 104 assignsa Home Address (HoA) to mobile node 102 from an IP subnetwork (“subnet”)that home agent 104 advertises into the IP network. This HoA of mobilenode 102 is fixed regardless of the location of mobile node 102.

In FIG. 1 Mobile Node 1 (MN1) 102 has registered in Region 1 with itslocal MIP home agent. A router with which the mobile node is currentlyattached is called the Foreign Agent (FA), which is foreign agent 106for MN1 102. The address of the Foreign Agent becomes the Care ofAddress (CoA) of mobile node 102. As illustrated in FIG. 1, inaccordance with MIPv4 a MIP tunnel is established from the home agent104 to foreign agent 106. Home agent 104 uses the MIP tunnel to forwardpackets to the MN1 102. Home agent 104 routes all traffic destined forMN1's 102 Home Address 1 (HoA1) through this tunnel, and foreign agent106 at CoA1 forwards the traffic to MN1 102. For the purposes of thisdiscussion, it is assumed that MIP Reverse Tunneling is always set tooff.

MN1 102 has also completed SIP registration with SIP server 108, whichhas associated MN1's SIP address (steve@carrier.com) with HoA1 withinthe SIP infrastructure. Similarly, MN2 110 has completed MIP and SIPregistration, which has established IP reachability for MN2 110 at HoA2via CoA2 and SIP reachability at his SIP address (sid@carrier.com).

When the mobile node registers with the home agent via the foreignagent, the home agent creates a binding between the HoA and CoA andcreates a tunnel for forwarding data packets addressed to HoA for themobile node using a standard technique called IP in IP tunneling. Anycorresponding node communicating with the mobile node regardless of thelocation of the mobile node, sends data packets to the HoA of the mobilenode. Since the home agent always advertises the subnet of the mobilenode, the data packets with a destination address equal to the HoA ofthe mobile node are always first routed to the home agent. The homeagent subsequently uses the IP tunneling mechanism discussed above toforward the data packets to the CoA of the foreign agent, which thenforwards the data packets to the appropriate link reaching the mobilenode.

In the standard MIPv4 mechanism it is evident that the communicationroute for data traffic from a corresponding node to a mobile node mustalways pass through the home agent and then be forwarded from the homeagent to the foreign agent using the current CoA associated with themobile node. This mechanism does not allow data traffic to flow alongthe shortest route from the corresponding node to the mobile node. Theun-optimized route for data traffic causes several deficiencies incommunication quality. First, because the route may be unnecessarilylong, the end-to-end transmission delay can be significantly longer thanwhen the route does not pass through a home agent. Longer delays maycause significant quality degradation in delay-sensitive services suchas VoIP and Push-to-talk over Cellular (PoC). Typically, delay in amobile network is longer than fixed networks. Thus, additional delay maybe particularly detrimental in mobile networks. Second, traffic to allthe mobile nodes registered with a home agent must pass through the homeagent causing congestion. In addition, a single home agent failure couldunnecessarily disrupt all traffic routed through the home agent. Thus,routing performance could be degraded in the network due to therequirement that a home agent is in the forwarding path for networksusing conventional MIPv4 routing. Third, more network bandwidth isrequired to carry traffic in a non-optimal way. More network bandwidthrequirement leads to more expensive network.

Using MIPv4, mobile-to-mobile bearer traffic is forwarded through theMIP tunnels setup using MIPv4 as illustrated in FIG. 2. This ensuresseamless mobility as the mobiles change their point of attachment.Specifically, the user datagram protocol (UDP) port numbers used by thereal-time protocol (RTP)/UDP and real-time control protocol (RTCP)/UDPstreams are negotiated and signaled by the SIP infrastructure betweenthe mobile nodes, and the mobile nodes' HoAs are used as the IPendpoints of these streams.

The next-generation mobile IP network protocol, commonly known as IPv6,addresses this particular problem by providing a “route optimization”mode. This mode requires the mobile node to register its current bindingwith the corresponding node. Packets from the corresponding node arerouted directly to the CoA of the mobile node. When sending a packet tothe IPv6 destination of the mobile node, the corresponding node checksits bindings for an entry for the packet's destination address. If acached binding for this destination address is found, the correspondingnode uses a new type of IPv6 routing header to route the packet to themobile node directly to the CoA indicated in this binding. Routingpackets directly to the mobile node's CoA allows the shortestcommunications path to be used.

This method for solving the un-optimized routing problem has threefundamental drawbacks. First, MIPv6 is not ubiquitously deployed and itmay take a long while to change the IPv4 and MIPv4 networks to IPv6 andMIPv6. Second, since MIPv6 is implemented in the network layer when amobile node changes its location all the different corresponding nodesthat may possibly communicate with the mobile node must be notifiedabout the current CoA of the mobile node so that all the correspondingnodes can refresh the binding. Thus, this method may suffer from a lackof scalability with respect to mobility. Third, MIPv6 route optimizationrequires that all mobile nodes and corresponding nodes trust each otherwith respect to the exchange of bindings containing routing information.Therefore, security could pose a challenge to MIPv6 implementations.

In view of the foregoing, there is a need for a method and system forroute optimization in an existing MIPv4 network without changing the IPnetwork infrastructure, functions and protocols. Furthermore, there is aneed for a system and method for route optimization in a mobileenvironment that is scalable and can be implemented on a peer-to-peerbasis and on selected services basis.

SUMMARY OF THE INVENTION

Systems and methods for handoff of mobile nodes are provided. Accordingto exemplary embodiments of the present invention, after establishing acall using standard MIPv4, first and second mobile nodes optimize thecall, thereafter conducting the call independent of home agents. Whenone of the mobile nodes initiates a handoff to another point ofattachment, communications directed to that mobile node are again routedthrough a home agent using a MIP tunnel. Upon completion of the handoffthe communications are again optimized, and are conducted independent ofhome agents.

Other objects, advantages and novel features of the present inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 is a block diagram of two mobile nodes that have bothsuccessfully completed both MIP and SIP registration in accordance withconventional procedures;

FIG. 2 is a block diagram illustrating the forwarding paths of theRTP/UDP and RTCP/UDP bearer streams between two mobile nodes in a VoIPcall based in conventional systems;

FIG. 3 is a block diagram illustrating the first step for detecting UDPports and source/destination IP addresses of the RTP/UDP and RTCP/UDPbearer streams between two mobile nodes in accordance with exemplaryembodiments of the present invention;

FIG. 4 is a block diagram illustrating the second step of the routeoptimization of exemplary embodiments of the present invention;

FIG. 5 is a block diagram illustrating the third step of the routeoptimization of exemplary embodiments of the present invention;

FIG. 6 is a block diagram illustrating the first step of the handoffprocedure in accordance with exemplary embodiments of the presentinvention;

FIG. 7 is a block diagram illustrating the second step of the handoffprocedure in accordance with exemplary embodiments of the presentinvention;

FIG. 8 is a block diagram illustrating the third step in the handoffprocedure in accordance with exemplary embodiments of the presentinvention; and

FIG. 9 is a flow chart illustrating an exemplary method for routeoptimization in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Exemplary embodiments of the present invention provide systems andmethods for route optimization of peer-to-peer applications in a mobileenvironment. This allows applications to overcome the restrictionimposed by MIPv4 that all traffic must pass through a home agent. Allpeer-to-peer applications will benefit from route optimization, but forthe purposes of illustration and not limitation, the present inventionwill be described below in connection with Voice over IP (VoIP). Inaccordance with exemplary embodiments of the present invention, mobilenodes communicate with each other using SIP for signaling and RTP formedia.

FIG. 3 illustrates the first step for detecting RTP/UDP and RTCP/UDPport numbers between the two foreign agents and the IP attachment pointsof the mobile nodes in accordance with exemplary embodiments of thepresent invention. Each IP attachment point foreign agent detectsRTP/UDP UDP port, RTP/UDP source IP address, RTP/UDP destination IPaddress, RTCP/UDP UDP port, RTCP/UDP source IP address and RTCP/UDPdestination IP address for each matching stream.

For security, the IP attachment point checks both the RTP/UDP andRTCP/UDP source IP addresses to ensure they are in the trusted rangebefore further processing. If the source IP addresses are legitimate,the IP attachment point foreign agent begins installing bindings foreach unique RTP/UDP or RTCP/UDP flow that is detected. These bindingsgovern the forwarding behavior of future flows.

As illustrated in FIG. 3, the bindings for flows from MN1 302 to MN2 304have the RTP/UDP/IP source address=HoA1, RTP/UDP/IP destinationaddress=HoA2, RTP/UDP port=A, RTCP/UDP/IP source address=HoA1,RTCP/UDP/IP destination address=HoA2 and RTCP/UDP port=A+1. The bindingsfor flows from MN2 to MN1 have the RTP/UDP/IP source address=HoA2,RTP/UDP/IP destination address=HoA1, RTP/UDP port=B, RTCP/UDP/IP sourceaddress=HoA2, RTCP/UDP/IP destination address=HoA1, and RTCP/UDPport=B+1.

FIGS. 4 and 5 are block diagrams illustrating the second and third stepsfor route optimization in accordance with exemplary embodiments of thepresent invention. Initially, port bindings for the incoming RTP/UDP andRTCP/UDP streams are established at the local point of attachment formobile nodes MN1 302 and MN2 304. After establishing the port bindings,the incoming RTP/UDP and RTCP/UDP streams are redirected via RTCP/UDPsignaling of the CoA.

These two flows trigger the insertion of RTP/UDP and RTCP/UDP bindingsat both IP attachment points. The bindings at the IP attachment pointwith CoA1 impose the following forwarding rules:

1) For RTP:

IF (RTP/UDP/IP destination IP address=CoA1) and

-   -   (RTP/UDP/IP source IP address=HoA2) and    -   (RTP/UDP/IP UDP port=B)

THEN (Forward to HoA1)

2) For RTCP:

IF (RTCP/UDP/IP destination IP address=CoA1) and

-   -   (RTCP/UDP/IP source IP address=HoA2) and    -   (RTCP/UDP/IP UDP port=B+1)

THEN (Forward to HoA1)

The bindings at the IP attachment point with CoA2 impose the followingforwarding rules:

1) For RTP:

IF (RTP/UDP/IP destination IP address=CoA2) and

-   -   (RTP/UDP/IP source IP address=HoA1) and    -   (RTP/UDP/IP UDP port=A)

THEN (Forward to HoA2)

2) For RTCP:

IF (RTCP/UDP/IP destination IP address=CoA2) and

-   -   (RTCP/UDP/IP source IP address=HoA1) and    -   (RTCP/UDP/IP UDP port=A+1)

THEN (Forward to HoA2)

Following the installation of the bindings described above, each mobilenode signals the other via RTCP/UDP signaling using a type 204application defined RTCP packet as specified in RFC 3550, “RTP: ATransport Protocol for Real-Time Applications.” This packet has thefollowing structure:

Referring now to FIG. 5, the destination IP address of the outgoingRTP/UDP and RTCP/UDP streams are now changed from the remote HoA to theremote CoA. This allows each mobile node to send his CoA to the othermobile node. Each mobile node then reacts by changing the destination IPaddress for the corresponding outgoing RTP/UDP and RTCP/UDP streams toredirect these streams directly to the remote CoA, bypassing the homeagent. The MIP tunnels are no longer needed and thus home agents 306 and308 may remove the tunnels.

An alternative method for a mobile node to notify its VoIP peer tochange the destination of its RTP/UDP and RTCP/UDP streams is to simplychange the source IP address of its outgoing RTP/UDP and RTCP/UDPstreams to the local CoA and have the VoIP peer respond by redirectingits outgoing RTP/UDP and RTCP/UDP flows to this CoA, thus bypassing thehome agent and optimizing the route. In this scenario, the bindingsinstalled within the IP attachment points would be formed based on theremote HoA embedded within the RTP header, not the source IP address ofthe RTP streams itself. This method is extensible to any flow for whichthere are bits available to embed the remote HoA.

FIGS. 6-8 are block diagrams illustrating the handoff procedure for MN2304 in accordance with exemplary embodiments of the present invention.Initially, incoming RTP/UDP and RTCP/UDP streams are redirected viaRTCP/UDP signaling of the CoA to MN1 302. Next, as illustrated in FIG.7, MN2 304 hands-off to a new IP point of attachment 310. This resultsin a CoA change. Accordingly, as illustrated in FIG. 8 port bindings atthe new local attachment point 310 are established for the incomingRTP/UDP and RTCP/UDP streams. Next, the incoming RTP/UDP and RTCP/UDPstreams are redirected via RTCP/UDP signaling of the CoA to MN1 302.

When a mobile node moves from one foreign agent to another foreign agentthe mobile node obtains CoA and new UDP ports at the new foreign agent.In order for standard hand-off procedures to work in a MIPv4 network,the first step of the original MIPv4 routing configuration should beperformed pursuant to FIG. 3. Before a mobile node hands off, it firstun-optimizes its incoming stream (i.e., routes communications throughthe home agent), then handoffs and finally re-optimizes its incomingstream (i.e., communicates independent of the home agent). This is shownin FIGS. 6-8. To un-optimize its incoming RTP/UDP and RTCP/UDP streams,MN2 304 sends an application specific RTCP packet containing HoA2, whichcauses MN1 302 to begin forwarding its corresponding outgoing RTP/UDPand RTCP/UDP streams to HoA2 via home agent 308 which sends the packetsto MN2 via the MIPv4 tunnel between home agent 308 and foreign agent312. After normal handoff processing, the new IP attachment point atCoA3 installs port bindings for the MN1-to-MN2 RTP/UDP and RTCP/UDPflows, and then MN2 304 sends another application defined RTCP packet toMN1 302 containing CoA3, which causes MN1 302 to begin forwarding itscorresponding outgoing RTP/UDP and RTCP/UDP streams directly to CoA3 asillustrated in FIG. 8, bypassing home agent 308.

FIG. 9 is a flow chart illustrating an exemplary method for routeoptimization in accordance with the present invention. Initially, mobilenodes MN1 and MN2 perform MIP and SIP registration (steps 902-908). MN1then initiates a call setup to MN2 (step 910) and a call is establishedbetween the mobile nodes via home agents (step 912). The attachmentpoints for mobile nodes MN1 and MN2 install the binding for the call(steps 914 and 920). MN1 then signals MN2 to redirect calls to MN1's CoA(step 916), and MN2 signals MN1 to redirect calls to MN2's CoA (step922). MN2 then redirects the call to MN1's CoA (step 918) and MN1redirects the call to MN2's CoA (step 924). Accordingly, the callbetween mobile nodes MN1 and MN2 is optimized (step 926).

When MN2 begins handoff from one point of attachment to another (step928), MN2 signals MN1 to redirect calls to MN2's HoA (step 930). MN2then hands-off to the new point of attachment (step 932) and signals toMN1 to redirect the call to MN2's CoA (step 934).

The peer-to-peer route optimization of the present invention decreaseslatency, provides a more efficient distributed transport utilization,and improves the call quality of VoIP and other delay sensitiveapplications. Although exemplary embodiments have been described inconnection with VoIP calls, the present invention is equally applicableto any type of communications between at least one mobile node andanother node.

The foregoing disclosure has been set forth merely to illustrate theinvention and is not intended to be limiting. Since modifications of thedisclosed embodiments incorporating the spirit and substance of theinvention may occur to persons skilled in the art, the invention shouldbe construed to include everything within the scope of the appendedclaims and equivalents thereof.

1. A method for communication between a first mobile node and a secondmobile node in a communication network implementing Mobile InternetProtocol version 4, the method comprising: assigning, by a first foreignagent of the communication network, a first Care of Address (CoA) to thefirst mobile node; establishing, by the communication network, acommunication link between the first mobile node and the second mobilenode via the first foreign agent and a home agent of the first mobilenode; detecting, by the communication network, at least one Real-TimeProtocol (RTP)/User Datagram Protocol (UDP) data flow from the secondmobile node to the first mobile node; installing, by the communicationnetwork, a binding for the at least one RTP/UDP data flow, the bindingcomprising a destination address for the at least one RTP/UDP data flow,wherein the destination address is the address of the home agent of thefirst mobile node; replacing, by the communication network, thedestination address of each binding with the first CoA assigned to thefirst mobile node; forwarding, by the communication network during afirst time period, the at least one RTP/UDP data flow from the secondmobile node to the first mobile node independent of the home agent ofthe first mobile node; replacing, by the communication network, thedestination address of each binding with the address of the home agentof the first mobile node, when the second mobile node hand-offs to asecond foreign agent; forwarding, by the communication network during asecond time period, the at least one RTP/UDP data flow from the secondmobile node through the home agent of the first mobile node, when thesecond mobile node hand-offs to the second foreign agent; assigning, bythe second foreign agent, a second CoA to the first mobile node, whenthe second mobile node hand-offs to the second foreign agent; replacing,by the communication network, the destination address of each bindingwith the second CoA assigned to the first mobile node, when the secondmobile node hand-offs to the second foreign agent; forwarding, by thecommunication network during a third time period, the at least oneRTP/UDP data flow from the second mobile node independent of the homeagent of the first mobile node, when the second mobile node hand-offs tothe second foreign agent; wherein the second time period is subsequentto the first time period and the third time period is subsequent to thesecond time period.
 2. The method of claim 1, wherein the first andsecond mobile nodes communicate control information using sessioninitiation protocol (SIP) signaling.
 3. The method of claim 2, whereinthe first and second mobile nodes exchange media using RTP signaling. 4.The method of claim 1, further comprising: transmitting, by the firstmobile node during the first time period, a redirection messageidentifying that communications to the first mobile node should be sentvia the home agent.
 5. The method of claim 1, further comprising:transmitting, by the first mobile node during the second time period, aredirection message identifying that communications to the first mobilenode should be sent independent of the home agent.
 6. The method ofclaim 1, wherein the first and second mobile nodes communicate usinginternet protocol (IP).
 7. The method of claim 6, wherein the internetprotocol is mobile internet protocol (MIP).
 8. The method of claim 7,wherein the mobile internet protocol is MIPv4.
 9. The method of claim 6,wherein the first and second mobile nodes communicate controlinformation using real-time transport control protocol (RTCP).
 10. Themethod of claim 9, wherein the first and second mobile nodes exchangemedia using real-time protocol (RTP) signaling.
 11. The method of claim1, wherein the first mobile node is supported by a first point ofattachment during the first time period.
 12. The method of claim 11,wherein the first mobile node is supported by the first point ofattachment and a second point of attachment during the second timeperiod.
 13. The method of claim 12, wherein the first mobile node issupported by the second point of attachment during the third timeperiod.